Ah, the example I provided needs to be run by itself (with no other config in the .circleci/config.yml file). That way it can establish a baseline of success for macos_exec.
The docker error is likely being introduced in one of the commands. *test-results-fastlane would be my first guess, but fatlane adhoc has a smell for me, too, because everywhere else the word is fastlane.
(General aside, I like to use our CLI tool when I’m setting up a new config, because running circleci-cli config process .circleci/config.yml gives me a fast first-pass check of how my config will compile.)